Some internal combustion engines utilize a compression device such as a turbocharger to increase engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to an exhaust manifold side of an engine and the compressor is coupled to an intake manifold side of the engine. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure (e.g. boost, or boost pressure) in the intake manifold and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, for example with a wastegate. An actuator may be operatively coupled via a linkage to a wastegate valve and driven to position the wastegate valve anywhere between a fully open position and a fully closed position (e.g., at a valve seat) to achieve the desired boost based on operating conditions. The actuator may be an electric actuator such as an electric motor, for example.
The turbocharger may be consistently exposed to high surrounding temperatures, for example due to proximate flow of hot exhaust gas. As such, a relatively long linkage may be employed to couple the wastegate valve to its associated actuator and reduce the proximity of the actuator to high temperatures to thereby protect the actuator from potential degradation arising from such high temperatures. Linkages of this type, however, may exhibit noise, vibration, and harshness (NVH) such as rattle during certain conditions—for example, during times at which the linkage remains relatively stationary or when an associated engine is idle. More generally, these issues may arise in control devices that employ servomechanisms to control relatively long linkages.
In some approaches to reducing NVH in a wastegate actuator, the wastegate valve is forced shut during certain operating conditions (e.g., during engine idle). In other approaches, a bias spring and/or other mechanical components (e.g., dampers) are coupled to the wastegate assembly at a location where vibration may be absorbed.
The inventors herein have recognized several issues with the approaches identified above. While NVH may be reduced for the approaches in which the wastegate valve is forced shut during certain operating conditions, the emissions and fuel economy exhibited by an engine employing such control may be adversely affected by back pressure generated by valve closure. In contrast, addition of a bias spring may increase the load imposed on the wastegate actuator, which may reduce the quality of boost control and increase the risk of actuator degradation due to high actuator temperatures caused by increased current levels drawn to overcome the increased load. Further, the addition of other mechanical components introduces added cost and potential points of failure, especially in locations where excessive heat is present.
Methods for operating a wastegate are thus provided.
In one example, a method of adjusting a linked valve actuator system comprises applying, in addition to feedback position control adjustments, a non-harmonic oscillation to an actuator of the linked valve actuator system.
In a more specific example, the non-harmonic oscillation is applied for a subset of wastegate valve lifts proximate, but not corresponding to, a valve seat of the linked valve actuator system.
In another aspect of the example, the non-harmonic oscillation is asinusoidal.
In yet another aspect of the example, the non-harmonic oscillation is periodic and has an overlay frequency determined based on a rattle frequency.
In still another aspect of the example, the rattle frequency is a period between successive times at which a wastegate valve of the linked valve actuator system makes contact with a valve seat of the linked valve actuator system.
In still further another aspect of the example, the overlay frequency is further determined based on a constant multiplied by the rattle frequency, the constant being an approximate ratio of Fibonacci numbers.
In the examples described above, NVH in a wastegate assembly may be reduced without forcing the wastegate valve closed and adversely affecting emissions and fuel economy. Moreover, the increased cost, actuator load, packaging space, and potential degradation associated with added parts may be obviated. In contrast to the addition of mechanical parts, the wastegate control routines of a vehicle may be easily augmented with the approaches described herein at any point of the vehicle lifetime, for example by updating instructions held in an engine controller. Thus, the technical result is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.